Sheet Material with Bend Controlling Grooves Defining a Continuous Web Across a Bend Line and Method for Forming the Same

ABSTRACT

A sheet of material ( 21, 61, 81 ) formed for control bending along a bend line ( 23, 63 ) while maintaining a continuous web of material ( 26 ) across the bend line ( 23, 63 ). The sheet has at least one groove ( 22, 62, 82 ) formed therein with a central groove portion ( 24, 64, 84 ) extending in the direction of and positioned proximate to a desired bend line ( 23, 63 ). The groove is formed with a continuous web of material ( 26 ) at a bottom of the groove ( 22, 62, 82 ) and has a configuration defining at least one bending strap ( 27, 67 ) extending across the bending line ( 23, 63 ) at the end of the groove with a centerline ( 28 ) of the bending strap ( 27, 67 ) oriented obliquely across the bend line ( 23, 63 ) so that a balancing of the forces during bending of the web along the central portion ( 24, 64, 84 ) of the grooves and bending of the oblique bending strap occur and control the location of bending of the sheet. A method of preparing a sheet of material ( 21, 61, 81 ) for bending while maintaining a continuous membrane ( 26 ) across the bend line ( 23, 63 ) is also disclosed.

RELATED APPLICATIONS

This application is a continuation-in-part application based upon aco-pending patent application Ser. No. 10/795,077, filed Mar. 3, 2004,and entitled Sheet Material with Bend Controlling Displacements andMethod for Forming the Same, which is a continuation-in-part applicationbased upon co-pending patent application Ser. No. 10/256,870, filed Sep.26, 2002, and entitled Method for Precision Bending of Sheet Materials,Slit Sheet and Fabrication Process, which was a continuation-in-partapplication based upon a co-pending parent application Ser. No.09/640,267, filed Aug. 17, 2002, and entitled Method for PrecisionBending of a Sheet of Material and Slit Sheet Therefor, now U.S. Pat.No. 6,481,259 B1.

TECHNICAL FIELD

The present invention relates, in general, to precision bending orfolding of sheet material, and more particularly, relates to preparingsheet material for bending by grooving the same so that a continuous webor membrane remains at the bottom of the groove, which web extendsacross the bend line when the sheet is bent.

BACKGROUND ART

The present method and apparatus are based upon sheet slitting andgrooving geometries disclosed in depth in the above set forth relatedapplications, which are each incorporated herein by reference in theirentireties. In these related applications several techniques ormanufacturing processes for forming slits and/or grooves that willprecisely control bending of sheet material are disclosed. The emphasisin these related applications is in connection with the use of slitswhich penetrate completely through the sheet of material. Both slits andgrooves or displacements can be provided which control bending by reasonof their configuration and the orientation of the bending straps at theends of the slits or grooves. For slit sheets, edge-to-face engagementof the sheet of material on opposite sides of the slits also is employedto achieve precision in the location of the bends.

These prior related applications also contemplate the use of grooving ofthe sheet material by various techniques in order to have a sheet ofmaterial in which there is a continuous web or membrane at the bottomsof the grooves. Such a web or membrane will allow the bent sheetmaterial to be fluid-tight across the bend line for applications whichrequire containment of a fluid and for use in electronic equipmenthousings as electromagnetic interference (EMI) shielding.

While in the prior related applications the emphasis was on controllingthe location of the bend precisely by using edge-to-face interengagementof the sheet material on opposite sides of the slits or grooves, it hasbeen discovered, and it is an important feature of the invention of thepresent application, that controlling of the positioning of the bendline on the sheet of material can be accomplished by a combination ofgroove location and bending straps configuration. Thus, a balancing ofbending forces can be set up that will control location of the bend linewithout the need for edge-to-face interengagement of the sheet materialon opposite sides of a slit. This grooving technique allows fluid-tightand EMI shielding housings to be constructed by bending sheet materialwith grooves and bending straps that control bending with sufficientprecision that complex housings for electronic products andfluid-containing applications can be achieved.

Grooving of sheet material in order to facilitate bending is broadlyknown in the patent literature. Thus, continuous grooves which do notpenetrate through a sheet have been used to cause bending of the sheetalong the approximate centerline of the grooves. Similarly,discontinuous grooves which are aligned along the bend line also havebeen used. Finally, grooves which are laterally andlongitudinally-offset along opposite sides of a bend line also have beenemployed as strategy for bending sheet material. Typical of the patentreferences disclosing these types of grooving techniques is U.S. Pat.No. 6,640,605 to Gitlin et al.

In the Gitlin et al. patent, however, the bending webs betweendiscontinuous grooves have centerlines which are parallel to the desiredbend line. This approach requires that the bending straps betweengrooves undergo substantial twisting, while the continuous webs at thebottom of the grooves are being bent. The approach results in a bendline which has less precision in its location than would be otherwisedesirable.

Accordingly, it is an object of the present invention to provide amethod of preparing sheet material for bending or folding along a bendline which is capable of producing structures that are fluid-tight, canact as EMI shielding structures, have improved appearance, haveadditional strength and are corrosion resistant.

Another object of the present invention is to provide a method ofpreparing sheet material for bending or folding, and the resultantsheet, and the bent or folded structure, which have improved versatilityin the ability to vary the bending characteristics and the materialswhich may be bent into structures.

A further object of the present invention is to provide a method forbending or folding a sheet material, the sheet therefor, and theresultant bent or folded structure formed using the sheet, which employgroove and bending strap configurations in order to control bend linelocation by balancing the forces in the bending straps during bending.

The grooved sheet material and method for preparing a sheet for bendingor folding of the present invention have other objects and features ofadvantage which will be set forth in more detail in, and will beapparent from, the following Best Mode of Carrying Out the Invention, asexemplified and illustrated by the accompanying drawing.

DISCLOSURE OF THE INVENTION

The method of preparing a sheet of material for bending or folding alonga bend line with a continuous membrane or web across the bend line, ofthe present invention is comprised, briefly, of the step of forming atleast one groove in the sheet of material with a central groove portionextending in a direction of, and positioned proximate to, the desiredbend line. The groove being formed during the forming step has acontinuous membrane of material across the bottom of the groove, or iscut through the sheet and has a layer of material laminated across thecut to result in a grooved, multi-layered sheet. The groove is formedwith a configuration and is positioned relative to the bend line todefine at least one bending strap at the end of the groove having acenterline oriented to extend obliquely across the bend line. Duringbending or folding of the sheet of material, a balancing of the forcesproduced while bending the membrane and bending the oblique bendingstrap occurs which controls the location of bending of the sheet ofmaterial. Most preferably, a plurality of laterally displaced groovesare formed in the sheet of material along the bend line on oppositesides of the bend line, which grooves also alternate and arelongitudinally shifted along the length of the bend line. During theforming step, each groove is formed with opposite groove end portionsthat diverge away from the bend lines so that the end portions oflongitudinally adjacent grooves define a plurality of bending strapshaving centerlines oriented to extend obliquely across the bend line.The forming step can be accomplished by removing material from the sheetto form the grooves or by displacing the sheet of material in athickness direction to form grooves on one side of the sheet, andadvantageously, to form ribs or ridges on the other side of the sheet.Laminated sheets as well as monolithic sheets may be grooved by cuttingthrough one layer of material with either post- or pre-lamination of asecond layer to the sheet.

In another aspect, a sheet of material is provided which is formed forcontrolled bending along a bend line with a continuous web of materialacross the bend line. The sheet of material comprises, briefly, a sheetof material having at least one groove formed therein with a centralgroove portion extending in a direction of, and being substantiallyparallel to, and positioned proximate to the desired bend line. Thegroove being further formed with a continuous web of material at thebottom of the groove and having a configuration defining at least onebending strap extending across the bend line at the end of the groove,with the strap having a centerline oriented to extend obliquely acrossthe bend line whereby a balancing of forces during bending of the webalong the central portion of the groove and bending of the obliquebending strap control the location of bending of the sheet of materialrelative to the bend line. Most preferably, a plurality of grooves areprovided with diverging groove end portions which define bending strapsat opposite ends of the grooves that extend in oppositely inclined,oblique orientations across the bend line so as to balance the bendingforces in a manner controlling location of the bend.

DESCRIPTION OF THE DRAWING

FIG. 1 is fragmentary top plan view of a sheet of material having bendcontrolling grooves formed therein in accordance with the presentinvention.

FIG. 2 is an enlarged, cross sectional view taken substantially alongthe plane of line 2-2 of FIG. 1.

FIG. 2A is a cross sectional view, corresponding to FIG. 2, of analternative embodiment of the present invention illustrating grooving ofa laminated sheet of material.

FIG. 3A is an enlarged, cross sectional view corresponding to FIG. 2with the sheet having been bent by 90 degrees from the position shown inFIG. 2 in a direction closing the grooves.

FIG. 3B is an enlarged, cross sectional view corresponding to FIG. 2with the sheet having been bent by 90 degrees from the position shown inFIG. 2 in a direction opening the grooves.

FIG. 4 is a top plan, fragmentary view, corresponding to FIG. 1 of analternative embodiment of a grooved/ribbed sheet material of the presentinvention.

FIG. 5 is a top plan, fragmentary view corresponding to FIGS. 1 and 4 ofstill a further alternative embodiment of a grooved/ribbed sheet of thepresent invention.

FIG. 6 is a cross sectional view taken substantially along the plane ofline 6-6 in FIG. 5.

FIG. 7 is a cross sectional view taken substantially along the plane ofline 7-7 in FIG. 5.

FIGS. 8A and 8B are end elevation schematic views, in cross section, ofa sheet of material being formed with a groove/rib by forming dies.

FIG. 8C is an end elevation view, in cross section, of the resultinggrooved/ribbed sheet of material.

FIGS. 9A and 9B are end elevation schematic views, in cross section, ofan alternative embodiment of a sheet being formed with a groove/rib byforming dies.

FIG. 9C is an end elevation view, in cross section, of the resultinggrooved/ribbed sheet of material.

BEST MODE OF CARRYING OUT THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. While the invention will be described in connection with thepreferred embodiments, it will be understood that the illustratedembodiments are not intended to limit the invention. On the contrary,the invention is intended to cover alternatives, modifications andequivalents, which may be included within the spirit and scope of theinvention, as defined by the appended claims.

Referring now to FIGS. 1, 2 and 3A, a sheet of material 21 can be seento be formed with at least one groove, and as illustrated, with aplurality of grooves 22 along a sheet bend line 23. Grooves 22 extendlongitudinally along, and are preferably placed on alternating sides of,bend line 23, with adjacent grooves being in a longitudinally shifted ordisplaced relationship, as one proceeds longitudinally along the bendline. Each groove 22 has a central groove portion 24 extendingsubstantially parallel to desired bend line 23, and the grooves defineat least one bending strap 27, usually between longitudinally adjacentgroove end portions. Straps 27 have centerlines 28 oriented to extendobliquely across bend line 23. The grooves, as best may be seen in FIG.2, do not penetrate completely through sheet 21, but instead define attheir bottoms a continuous web or membrane 26 which enables thesubsequently folded or bent sheets to present a fluid-tight barrier.

The transverse cross sectional shape of grooves 22 does not have to beU-shaped, as illustrated in FIG. 2, but instead can be V-shaped, arectangular shape or various other possibilities within the scope of thepresent invention. Similarly, the depth of the groove and the thicknessof web 26 can vary, as will be illustrated and described below.

In a broad aspect, therefore, the grooves are formed so that theycontrol bending of the sheet about bend line 23 by a balancing of theforces during bending. As best may be seen in FIG. 2, groove 22 a, atwhich the cross section is taken, will tend to bend along a groove bendline 23 a which will be located where web 26 has a minimum thickness.Similarly, groove 22 b, the next or longitudinally adjacent groove, willtend to bend about groove centerline 23 b, again at a position at whichweb 26 at the bottom of groove 22 b has a minimum thickness. Obliquelyoriented bending straps 27 have centerlines 28 which preferably areskewed along bend line 23 in opposed directions, in a manner which canbest be seen in FIG. 1. Thus, the lateral offset of the grooves alongthe bend line, as well as bending straps 27 at opposite ends of eachgroove, tend to pull the sheet down against central groove portions 24of the alternating grooves in a balanced manner. Straps 27 are both bentand twisted during bending of the sheet, but they are balanced at eachend of each groove so that the resultant bend line 23 for sheet 21 willbe approximately located equidistant between bend lines 23 a and 23 b.As the jog distance between the groove centerlines 23 a and 23 bdecreases, groove bend lines 23 a and 23 b tend to be superimposed oversheet bend line 23. As the jog distance between the grooves increases,sheet bend line 23 will tend to stay, on average, equidistant betweenthe two groove bend lines, provided that the jog distance between thegrooves is not too great. As the jog distance between grooves 23 a and23 b increases, there will come a point at which a plurality of bendlines will form, rather than a single sheet bend line 23. The actualcenterline of bending of straps 27, from one groove to another, becomesrelatively complex, but for most jog distances, including negative jogdistances, the location of sheet bend line 23 will be predictablypositioned between the groove bend lines 23 a and 23 b.

It is believed that the lateral jog between grooves can be reduced tothe point that there is no bending strap between side-by-side touchinggrooves, but there is a lateral jog or distance between the greatestdepth of two side-by-side grooves. In that case (not shown in thedrawing), the greatest depth of each groove will produce thinnest websor weakened planes that are laterally offset. The sheet will attempt tobend locally at each weakened plane, which planes are laterally offsetin an alternating fashion from each other along the bend line. Thus, abalancing of forces occurs so that bending or folding will be controlledby the lateral jog between alternating groove bottoms and will occur onthe desired bend line. A special case of this approach of using abalancing of the web bending forces without having bending straps wouldbe a continuous wave or longitudinally undulating groove whichalternatively crosses back and forth along the bend line.

Returning now to the illustrated embodiments, in FIG. 3A, sheet 21 hasbeen bent in a direction closing grooves 22, while in FIG. 3B, sheet 21has been bent in an opposite direction opening grooves 22. Both types ofbends are within the spirit and scope of the present invention, and theselection as between the two types of bends often will be made basedupon the appearance effects. Both types of bends result in a membrane orweb 26 that extends across the bend and provides a fluid-tight barrierof the type which is highly desirable for many applications. Moreover,the membrane which extends across the bend can act as a substrate forsupport of, for example, electrical circuit path or trace that is laiddown or deposited on the sheet across the bend. Still further, the webwhich extends across the bend adds to the strength of the bending strapsso that an improvement in the overall bend strength can be realized.

Referring further to FIG. 3A, during the bending process, it should alsobe noted that bending straps 27 at opposite ends of grooves 22 will pullor snug the side of the sheet between arcuate groove end portions 30down against central groove portion 24. Thus, sheet 21 is pulled down atarea 33 and an inner side 31 of the sheet will slip over the inner side32 on the opposite side of groove 22 a. This pulling down of section 33during the bend occurs on alternate sides of the bend line along thelength thereof. This again effects a balancing of the tension forces inthe straps and webs so as to enhance control of the location of sheetbending, and it enhances the overall strength of the bend when the bentstructure is loaded.

In FIG. 3B a similar effect occurs when the sheet is bent in theopposite direction. The areas 33 of the sheet between arcuate groove endportions 30 are pulled slightly up or toward a central groove portion 24on the opposite side of the bend line 23. This occurs at alternatingcentral portions 24 along bend line 23 and again is therefore balancedand makes more predictable the location of bend line 23.

There are numerous ways of grooving sheet material in order to practicethe present invention, and it will be understood that any process whichis capable of grooving a sheet of material is regarded as being withinthe spirit and scope of the present invention. Some processes, however,are particularly well suited to specific applications. Grooves 22, asillustrated in FIGS. 1, 2, 3A and 3B, are formed by removing materialfrom sheet 21, and the amount of material removed has a depth dimensionless than the thickness dimension of the sheet. The grooves 22 can beadvantageously formed, for example, using milling or routing/machiningprocesses, which are particularly well adapted for use in groovingthicker metal sheets. A single point tool also can be employed. Etching,chemical milling and plasma or ion milling can be used advantageouslyfor thinner sheet material and can be used for nano-technologyapplication on metallic and non-metallic sheets. Laser or water jetgroove forming can be used, although controlling the depth ofpenetration of lasers and water jets requires care.

The width and depth of grooves 22, as well as the lateral jog distancebetween grooves, can be varied. A typical starting place is a groovehaving a width dimension approximately equal to the thickness dimensionof the sheet of material and a depth dimension of about 80 to about 90percent of the thickness dimension of the sheet of material. Thesedimensions can be varied considerably, depending upon the particularapplication and the strength needed for the part or product. In theillustrated groove pattern of FIGS. 1 and 2, it will be seen that thejog distance between centerlines 23 a and 23 b is approximately equal tothe width dimension of the grooves so that sheet bending line 23 isaligned at the aligned edges of alternating grooves 22.

The process and apparatus of the present invention can be used forbending metallic, non-metallic and composite sheet material, as well aslaminated layers of metallic and non-metallic materials. Thus, thepresent invention is particularly well suited for use in thesemiconductor industry. As the sheet material becomes thinner, formingthe grooves using a chemical etching process also becomes morepractical, and eventually one of the more preferable techniques,especially in nano-technology applications.

FIG. 2A illustrates an alternative embodiment of the present inventionin which a laminated sheet 21′ has been grooved in accordance with thepresent invention. Sheet 21′ is comprised of an upper sheet or layer 20to which a lower sheet or layer 25 is adhered, bonded or laminated, forexample, by an adhesive or thermal bonding process. Layer 20 could, forexample, be a sheet of a material having poor ductility, such as abrittle fiberglass or plastic, while layer or sheet 25 could be a veryductile sheet or layer, such as a ductile metal.

Sheet 20 is shown with grooves 22 a′ and 22 b′ which preferably havebeen chemically etched into a metal or plastic sheet. When the etchingprocess reaches the top surface 19 of sheet 25, etching can be stopped,for example, by neutralizing the etching chemicals or by the adhesivelayer which bonds layers 20 and 25 together, or by the chemicalinertness of the material of layer 25, as compared to the chemicalreactivity of layer 20. Grooves 22 a′ and 22 b′ correspond to grooves 22a and 22 b in FIGS. 1 and 2 and have groove bend lines 23 a′ and 23 b′with sheet bend line 23′, as described above for FIGS. 1 and 2.

The grooved laminate sheet 21′ will have bending webs 26′ that areductile and facilitate bending in the same manner as shown in FIGS. 3Aand 3B, only the sheet will be a laminated sheet.

It also will be obvious to one skilled in the art that laminated sheet21′ of FIG. 2A can be grooved using any or all the techniques set forthabove instead of etching. Various combinations of materials can belaminated together to produce various strength, ductility conductivity,erosion resistance and other effects which will not be easily achievedwhen a single layer of material is used. Laminated sheets also may have,as one form, the mere adherence of a layer of a flexible coating 25,such as, a paint, epoxy, dip brazing layer, etc., which again can haveadvantages when layer 20 is relatively thin.

While laminating is described above as a pre-grooving step, it will alsobe understood that layer or sheet 20 can be cut through to form slitsand layer 25 laminated or adhered to layer 20 after the slitting occurs.This converts the slits to grooves in which there is a continuousmembrane or web 26 across the bottom of what was slits. Laminated sheet21′ also could have more than two layers, and grooves 22 a′ and 22 b′could penetrate less than all the way through upper layer 20 or intolower layer 25, depending on the bending effects desired.

Whether laminated or monolithic sheets are grooved in accordance withthe present invention, the grooved sheets with continuous webs can beused in many fluid-tight structures. Thus, hermetically sealedenclosures can be crated to contain partial vacuums or positivepressures. EMI shielded structures can be created, as can boats, heatexchangers, catalytic arrays, vessels and fluid reservoirs, to name onlya few of many fluid-tight possibilities.

Additionally, the grooved bent sheets of the present invention, withtheir continuous webs across the bends, are particularly well suited foruse in printed circuit board (PCB) or printed wiring board (PWB)applications because the continuous webs give greater flexibility in thelocation of conductive paths on the sheet material. While bending strapscan also function as support surfaces for PWB or PCB paths when thesheets are slit and discontinuous at the slits, having a continuous webacross the bends allows flex circuit paths or flex circuit traces inmore locations on crowded boards. Additionally, electrical component ormicro device housings, which are mounted to PWB or PCB, also may beadvantageously formed using the sheet grooving technique of the presentinvention.

As shown in FIGS. 5, 6, 7, 8C and 9C, grooves are formed on a front sideof the sheet material and ribs are formed on the back side of the sheetby displacing the sheet of material in the thickness direction withoutsevering or penetrating through the sheet. FIGS. 8A-8C and 9A-9Cillustrate two techniques for forming the bend line controllinggrooves/ribs by displacing the sheet of material. Such displacement canbe effected, for example, by stamping, punching and roll forming.

In FIGS. 8A-8C, sheet 41 is positioned for grooving/ribbing usingstamping, punching or roll-forming dies, schematically shown at 42 and43. In FIG. 8A the sheet is placed between dies 42 and 43, and in FIG.8B the dies are closed so that the male die 42 displaces the sheet ofmaterial into the female die 43, with the result being shown in FIG. 8Cas a sheet 41 having a groove 44 on a front or upper side of sheet 41and a ridge or rib 45 on the back or downward side of sheet 41. Thegroove/rib will advantageously take the longitudinal shape of grooves 22as shown in FIG. 1, although the dies and groove/rib are onlyschematically shown in FIGS. 8A-8C as a cross section through thecentral portion of the groove/rib. As will be seen, bottom 46 of groove44 is formed as a continuous web or membrane, which again will act as afluid-tight barrier and a continuous surface across the bent sheet.

In FIGS. 9A-9C, a sheet 51 is being formed by dies 52 and 53, but inthis case, the depth of the groove/rib forming surfaces 57 of female die53 is less than that in FIG. 8A, with the result that the male die 52will plastically deform and thin web 56 of groove 54. This can best beseen by comparing FIG. 9C to FIG. 8C. Such a groove/rib will have awork-harden web 56 with some increased brittleness. However, workhardening of web 56 will vary with the ductility of the material beingformed, and it can be influenced by heat or chemical treatment, ifrequired. Thinner web 56, if the work hardening is neutralized, willgenerally produce a somewhat easier sheet to bend.

Heat and/or chemical treatment of the webs at the bottoms of groovesformed in accordance with the present invention can be used to influencethe bending or folding forces, regardless as to whether or not the webshave been work hardened by the groove forming process. Thus, formetallic and non-metallic materials localized applications of heat orchemicals can be used to anneal or soften the webs and/or bending strapsto thereby reduce force required to bend or fold the sheet. Metals withhigh conductivity will tend to rapidly conduct heat away from the areabeing annealed, but differential heating or heating and simultaneouscooling or quenching could be employed.

Similarly, chemical softening, particularly of non-metallic or compositesheets also may be feasible, with masking and/or chemical neutralizationbeing used to control the area affected. Chemical softening may be moreeasy to control than heat treatment since the chemicals will notdisperse as quickly as heat is conducted away from the site at which itis applied.

Another way of producing thinned web 56 of FIG. 9C is to use acombination of deforming and removing of material. Thus, the groovedsheet 41 can be abrasively treated or ground on its outside surface soas to thin the thickness of web 46 to that of web 56. Such grinding willinvolve generation of heat that affects ductility, but generallygrinding to produce a reduced web thickness will be an approach in whichthe ductility and malleability of web 46 will not be as adverselyeffected as in the process of FIGS. 9A-9C.

As will be seen in FIGS. 8C and 9C, grooves 44 and 54 have a depthdimension which is greater than the thickness dimension of sheets 41 and51. It also is possible to displace sheets 41 and 51 by an amount thatis less than the thickness dimensions of the sheets. This step will alsoproduce ridges or ribs 45 and 55 on the back side of the sheets, but ifribs are not required for stiffness, as set forth below, the back sidesof such sheets can have the ribs or ridges ground off flush to the restof the back side of the sheet. This thins webs 46 and 56 and eliminatesthe back side ribs 45 and 55.

Turning now to FIG. 4, a sheet grooving and ribbing scheme is shown inwhich a plurality of grooves/ribs 62 are formed in sheet 61, with eachgroove/rib again having a central portion 64 which is generally parallelto a bend line 63. End portions 70 diverge away from bend line 23 todefine bending straps 67 that have centerlines that are oblique to thebend line 63. In the embodiment shown in FIG. 4, grooves/rib 62 take theform as shown in FIGS. 8C or 9C, namely, the sheet material has beengrooved by displacement of the sheet so that the front side of the sheetis grooved at 44 and 54, for example, and the back side of the sheet hasa corresponding rib or ridge 45 and 55 which protrudes outwardly of thesheet. When groove/ribbed end portions 70 of the sheet extend asignificant distance laterally away from the bend line, the ribs formedon the back side of sheet 61, in effect, stiffen the sheet proximatestraps 67 and force straps 67 to bend in the desired location bysupporting the sheet against bending in other locations. In the mostpreferred form, groove/rib end portions 70 extend away from the bendline by distance equal to between about 5 to about 10 times thethickness dimension of the sheet of material.

In FIGS. 5, 6 and 7, a further alternative embodiment of thegrooved/ribbed sheet of FIG. 4 is shown in which a transitional areas 85between the central groove/rib portions 84 and the end groove/ribportions 90 of grooves/ribs 82 have an increased width dimension. Thisaddition area at 85 allows sheet 81 to bend without displacement orpuckering in the thickness dimension of the sheet at the transitionbetween the grooves/ribs and the straps.

While the direction of bending of the groove/rib sheet of the presentinvention can be used to enhance the appearance of the inside or theoutside of the bent structure to be formed, it is also possible to useflexible coatings in combination with the present sheet groovinginvention. Thus, a thin coating of a flexible material, such as an epoxyor paint can be placed on the grooved sheet prior to bending and thenthe sheet bent into the desired structure. The adhered coating acrossthe webs at the bottom of the grooves and the straps will flex toaccommodate the bend without fracturing or having the coating continuityimpaired.

The primary advantage of the apparatus and method of the presentinvention is that a continuous web or membrane will exist across thebend line to fluid-tight or EMI applications, but the present groovingtechnique can be used for other applications when it is expected orcontemplated that web 26 will fracture upon folding of the sheet. Evenwhen the grooves are too wide for edge-to-face engagement, whichproduces the high precision material folding as disclosed in theabove-referenced related applications, the grooving technique of thepresent invention will produce bending in predictable locations withsufficient accuracy for many applications that do not require afluid-tight membrane across the fold.

Having described the apparatus of the present invention, the method ofpreparing a sheet of material for bending along a bend line with acontinuous membrane across the bend line, can be described. The presentmethod includes a step of forming at least one groove in a sheet ofmaterial, with a central portion of the groove extending in a directionof the desired sheet bend line. The groove is formed with a continuousmembrane or web of material across the bottom of the groove and isfurther formed with a configuration, and is positioned relative to thebend line, to define at least one bending strap at the end of the groovehaving a centerline oriented to extend obliquely across the bend line.The resulting sheet will experience a balancing of bending forcesproduced during bending of the membrane and bending of the obliquebending strap, which balanced forces control the location of bending ofthe sheet of material. The thin web at the bottom of the groove willprovide a weakened plane at which bending will occur along the centralportion of the groove, and the end portions of the groove define a strapwhich will be configured, so as to balance the strap bending forces andpredictably position the bend line on the sheet of material. Alternatingobliquely oriented straps defined by longitudinally adjacent diverginggroove end portions will insure such a balancing of bending forces and,accordingly, the present method also preferably includes the step offorming the groove to define such straps.

The present method can be accomplished using monolithic sheets (FIGS. 1,2, 3A, 3B) or laminated sheets (FIG. 2A) by removing material from thesheet to form the grooves, or by displacing the sheet in a thicknessdirection without severing or penetrating the sheet. In one embodiment,the sheet is displaced outwardly to form ribs or ridges on the back sideof the sheets, and the end portions of the grooves of the back side ofthe sheet provide stiffening ridges which extend away from the groove bya distance which reinforces and controls bending of the bending straps.The removal of material can be accomplished using milling, routing,chemical etching, ion milling, laser cutting or water jet cutting of thesheet of material, and displacing of grooves can be accomplished bystamping, punching or roll-forming of the sheet of material. As afurther step in the present invention, after the sheet is grooved, thestep of bending the sheet of material will be performed to bend thecontinuous webs and to bend and twist the obliquely oriented bendingstraps. The sheet can be bent or folded in a direction closing thegrooves or in a direction opening the grooves, within the spirit andscope of the method of the present invention.

1. A sheet of material formed for controlled bending along a desiredbend line with a continuous web of material across the bend linecomprising: a sheet of material having at least one groove formedtherein with a central groove portion extending substantially parallelto and positioned proximate to the bend line, the groove further havinga continuous web of material defining a bottom of the groove and havinga configuration defining at least one bending strap extending across thebend line at an end of the groove, the bending strap having a centerlineoriented to extend obliquely across the bend line, whereby a balancingof the forces during bending of the web along the central portion of thegroove and bending of the oblique bending strap controls the location ofbending of the sheet of material relative to the bend line.
 2. The sheetof material as defined in claim 1 wherein, the groove is formed byremoving material from the sheet of material, and the groove has a depthdimension less than a thickness dimension of the sheet of material. 3.The sheet of material as defined in claim 1 wherein, the groove isformed by displacing the sheet of material in a thickness direction ofthe sheet of material without severing the sheet of material.
 4. Thesheet of material as defined in claim 1 wherein, the groove has an endportion diverging away from the bend line to define the bending strap,and the sheet of material on a side opposed to the diverging end portionis displaced out of the plane of the sheet of material and against thecentral groove portion during bending.
 5. The sheet of material asdefined in claim 1 wherein, a plurality of grooves with continuous websat the bottoms of the grooves are formed in the sheet of material alongand proximate to the bend line on sides of the bend line which alternatealong the length of the bend line, each of the grooves being formed withopposite end portions that diverge from the bend line so thatlongitudinally adjacent end portions define a plurality of bendingstraps extending across the bend line at the ends of the grooves andhaving strap centerlines that are obliquely oriented to the bend line.6. The sheet of material as defined in claim 5 wherein, the centerlinesof the straps defined by the end portions of the grooves extend inoppositely inclined directions so that bending straps at the oppositeends of each groove pull against the forces resulting from bending thewebs at the bottoms of the grooves to control bending.
 7. The sheet ofmaterial as defined in claim 6 wherein, the bending straps are formedand positioned to pull the sheet of material down out of the plane ofthe sheet of material on alternating sides of the bend line.
 8. Thesheet of material as defined in claim 5 wherein, the grooves arepositioned with the bottoms of the central portions of alternatinggrooves laterally equally spaced from opposite sides of the bend linefor bending of the sheet of material along bend line segments that arealternatively laterally spaced from the bend line with bent and twistedbending straps extending across the bend line between the bend linesegments.
 9. The sheet of material as defined in claim 3 wherein, thedisplaced grooves form protruding ridges on the back side of the sheetof material, and the grooves and ridges have end portions extending awayfrom the bend line in a near normal orientation to the bend line, andthe end portion ridges extend away from the bend line by a distancesufficient to insure localized bending of the sheet of material at thebending straps and along the central portions of the grooves.
 10. Thesheet of material as defined in claim 9 wherein, the end portion ridgesextend away from the bend line by a distance equal to between about 5and about 10 times the thickness dimension of the sheet of material. 11.The sheet of material as defined in claim 5 wherein, the grooves areeach formed with an increased width dimension at areas of transitionbetween the central portions and the end portions of the grooves. 12.The sheet of material as defined in claim 5 wherein, the grooves areformed by removing material from the sheet of material, and the grooveshave a depth dimension less than a thickness dimension of the sheet ofmaterial.
 13. The sheet of material as defined in claim 5 wherein, thegrooves are formed by displacing the sheet of material in a thicknessdirection without severing through the sheet of material.
 14. The sheetof material as defined in claim 5 wherein, the grooves are formed bydisplacing the sheet of material in the thickness direction and byremoving material from the thickness dimension of the grooves at thebottoms of the grooves.
 15. The sheet of material as defined in claim 14wherein, the material removed at the bottom of the grooves is removedfrom a back side of the sheet of material.
 16. The sheet of material asdefined in claim 13 wherein, the grooves are displaced into the sheet ofmaterial by a depth dimension greater than the thickness dimension ofthe sheet of material.
 17. The sheet of material as defined in claim 5,and a flexible coating of material adhered to the grooved side of thesheet of material.
 18. The sheet of material as defined in claim 1wherein, the sheet of material is comprised of at least two layers ofsheet material adhered together to form a laminated sheet.
 19. The sheetof material as defined in claim 18 wherein, the groove extendscompletely through an upper layer to a lower layer of the laminatedsheet.
 20. The sheet of material as defined in claim 19 wherein, thelower layer of the laminated sheet has greater ductility than the upperlayer.
 21. The sheet of material as defined in claim 19 wherein, thegroove is chemically etched into the upper layer of the laminated sheet.22.-29. (canceled)
 30. A method of preparing a sheet of material forbending along a bend line with a continuous membrane extending acrossthe bend line comprising the step of: forming at least one groove in asheet of material with a central groove portion extending in a directionof the bend line, the groove having a continuous membrane of materialextending across the bottom of the groove with a configuration and at aposition relative to the bend line to define at least one bending strapat an end of the groove having a centerline oriented to extend obliquelyacross the bend line whereby a balancing of the forces produced inbending the membrane and bending the oblique bending strap control alocation of bending of the sheet of material, wherein during the formingstep, a plurality of longitudinally extending grooves are formed in thesheet of material along the bend lines on sides of the bend line whichalternate along the length of the bend line, during the forming step,forming each groove with opposite end portions that diverge away fromthe bend line so that end portions longitudinally adjacent groovesdefine a plurality of bending straps extending across the bend line andhaving centerlines oriented obliquely to the bend line, during thedisplacing step, displacing the sheet of material to form grooves in afront side of the sheet and to form ribs in the back side of the sheet,and during the displacing step, forming the ribs with end portions thatextend away from the bend line in a near perpendicular orientationthereto for a distance equal to between about 5 and about 10 materialthicknesses. 31.-42. (canceled)
 43. A method of bending a sheet ofmaterial to produce a fluid-tight bent structure comprising the stepsof: forming a plurality of grooves in a sheet of material along a bendline with each groove having a continuous web of material extendingacross a bottom thereof and each groove having a central portionextending in a direction of the bend line and end portions extendingaway from the central portion and diverging away from the bend line, thegrooves being positioned along the bend line with the end portions oflongitudinally adjacent grooves diverging away from opposite sides ofthe bend line with strap centerlines that extend obliquely across thebend line in oppositely inclined directions; and bending the sheet ofmaterial to bend the continuous webs and to bend and twist the obliquelyoriented bending straps intermediate the grooves to form the bentstructure, wherein during the bending step, employing a balancing of theforces produced during bending of the webs and bending the straps tocontrol the location of the bending relative to the bend line, furtherwherein, the forming step is accomplished by displacing the sheet ofmaterial in the thickness direction to form the grooves in one side ofthe sheet of material and to form ridges in the other side of the sheetof material. 44.-49. (canceled)
 50. A fluid-tight structure comprising:a sheet of material grooved to control bending of the sheet along aplurality of bend lines, with each bend line having a continuousmembrane extending thereacross, the sheet being bent along the bendlines to form an enclosure and being sealed along a juncture between twoportions of the sheet to complete the fluid-tight enclosure.
 51. A sheetof material formed for controlled bending along a desired bend line witha continuous web of material across the bend line comprising: a sheet ofmaterial having at least one groove formed therein with a central grooveportion extending substantially parallel to and positioned proximate andlaterally spaced from the bend line, the groove further having acontinuous web of material defining a bottom of the groove with at leasttwo areas of minimum thickness in longitudinal and laterally spacedapart positions providing laterally spaced apart weakened planes wherebya balancing of the forces during bending of the web along the groovecontrols the location of bending of the sheet of material relative tothe bend line.